The present invention relates to a method of fabricating a semiconductor device. Particularly, it relates to a method of fabricating a semiconductor device to which QFN (Quad Flat Non-Leaded Package) is applied.
In recent years, QFN has been proposed as a structure for miniaturizing semiconductor devices. In the semiconductor device to which the QFN is applied, a surface 101a of a lead 101 for connection to the exterior is exposed in a state where it is nearly flush with a reverse surface 102a of a package 102, as shown in FIGS. 3A and 3B. The connection to the exterior can be achieved by joining the exposed surface 101a of the lead 101 to an external electrode formed on a mounting board, for example. That is, in the QFN-type semiconductor device, the lead 101 does not project from the package 102. Consequently, the occupied area of the QFN-type semiconductor device on the mounting board and the height thereof can be made smaller, as compared with those of a typical semiconductor device having a lead pin projecting from a package.
In the QFN-type semiconductor device, a semiconductor chip 103 is mounted on an island 104 of a lead frame, as shown in FIG. 4A. The mounted semiconductor chip 103 and the lead 101 are connected to each other by a bonding wire 105. After an assembly of the semiconductor chip 103 and the lead frame is thus formed, the assembly is set in a metal mold 106 to carry out a resin sealing step, thereby making it possible to obtain the QFN-type semiconductor device.
The metal mold 106 used for the resin sealing step comprises a lower metal mold 107 having a fitting recess 107a in which the lead 101 can be fitted formed therein and an upper metal mold 108 having a cavity 108a capable of containing the assembly formed therein. In the resin sealing step, the assembly is set in the lower metal mold 107 with the lead 101 fitted in the fitting recess 107a of the lower metal mold 107. Thereafter, the set assembly is covered with the upper metal mold 108 so as to be contained in the cavity 108a. In this state, protective resin is injected between the lower metal mold 107 and the upper metal mold 108. After the injected protective resin is hardened to form the package 102, the assembly sealed into the package 102 is taken out of the metal mold 106. Consequently, the QFN-type semiconductor device as shown in FIG. 4B is completed.
In the QFN-type semiconductor device fabricated in the above-mentioned manner, so-called resin burrs may occur. That is, in the resin sealing step, the protective resin injected between the lower metal mold 107 and the upper metal mold 108 enters a portion between the fitting recess 107a of the lower metal mold 107 and the lead 101 fitted in the fitting recess 107a. Consequently, the protective resin 109 adheres to the surface 101a, exposed to a reverse surface of the package 102, of the lead 101, as shown in FIG. 4B.
The exposed surface 101a of the lead 101 is an external joint surface which is joined to the external electrode formed on the mounting board, for example. If the protective film 109 adheres to the exposed surface 101a, therefore, the electrical connection between the semiconductor device (the semiconductor chip 103) and the exterior may not be achieved.
An object of the present invention is to provide a method of fabricating a semiconductor device capable of preventing protective resin from adhering to an external joint surface of a lead.
Another object of the present invention is to provide a method of fabricating a semiconductor device having no protective resin adhering to an external joint surface of a lead, being thin, and having good heat dissipation properties.
Still another object of the present invention is to provide a semiconductor device being thin and having good heat dissipation properties.
The present invention relates to a method of fabricating a semiconductor device in which an external connection surface of a lead electrically connected to a semiconductor chip is exposed in a state where it is nearly flush with a surface of a package. The method according to the present invention comprises a resin sealing step for integrally forming a sealing portion for sealing the semiconductor chip and a protective resin layer almost covering the external connection surface using a material for the package, and a resin removing step for removing at least a part of the protective resin layer, to expose the external connection surface. The resin removing step may be a grinding step for grinding the protective resin layer. Further, the resin removing step may be the step of removing at least a part of the protective resin layer by etching.
More specifically, the present invention relates to a method of fabricating a semiconductor device in which a semiconductor chip is electrically connected to one surface of a lead, and the other surface of the lead is exposed in a state where it is nearly flush with a surface of a package for electrical connection to the exterior. The method comprises a resin sealing step for forming an integral protective resin layer for almost covering the one surface and the other surface of the lead and sealing the semiconductor chip using the material for the package, and a resin removing step for removing at least a part of the protective resin layer from the other surface of the lead to expose the other surface of the lead. In this case, the other surface of the lead corresponds to the external connection surface.
It is preferable that the protective resin layer has a flat surface approximately parallel to the external connection surface and being of approximately the same size of the plane size of the semiconductor device.
It is preferable that the protective resin layer is formed so as to cover at least an inner edge of the semiconductor device on the external connection surface.
According to the present invention, it is possible to obtain a semiconductor device by integrally forming the sealing portion for sealing the semiconductor chip and the protective resin layer for almost covering the external connection surface and then, removing at least a part of the protective resin layer to expose the external connection surface. Consequently, the possibility that protective resin which is the material for the package remains adhering to the external connection surface of the lead is eliminated. Accordingly, the semiconductor device fabricated in this method can achieve good electrical connection to the exterior when the external connection surface of the lead exposed from the package is joined to an external electrode formed on a mounting board, for example.
According to this method, at least a part of the protective resin layer almost covering the external connection surface of the lead is removed, to expose the lead. Even if the removal is performed by grinding, therefore, a large force may not be exerted on the lead, and the lead may not be stripped from the package.
The electrical connection between the lead and the semiconductor chip may be achieved by carrying out, before the resin sealing step, a mounting step for mounting the semiconductor chip on an island of a lead frame; and a bonding step for bonding the semiconductor chip mounted on the island and the lead to each other.
In one embodiment of the present invention, the semiconductor chip is mounted with an inactive surface, which is opposite to an active surface having functional devices formed thereon, joined to the island. Both the active surface of the semiconductor chip and a joint surface of the island and the semiconductor chip are arranged on one side of a plane including the external connection surface.
In another embodiment of the present invention, the active surface of the semiconductor chip is arranged on one side of a plane including the external connection surface, and a joint surface of the island and the semiconductor chip is arranged on the other side of the plane including the external connection surface. In this case, in the resin removing step, the protective resin layer and the island are removed by grinding or the like. Accordingly, the inactive surface of the semiconductor chip is exposed.
According to this method, the protective resin layer and the island are removed, thereby making it possible to further thin the semiconductor device.
The semiconductor device fabricated by this method can efficiently dissipate heat from the semiconductor chip because the inactive surface of the semiconductor chip is exposed from the package.
When the active surface of the semiconductor chip is directed upward, the joint surface of the island and the semiconductor chip is positioned below the plane including the external connection surface, and the active surface of the semiconductor chip is positioned above the plane including the external connection surface.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following description of the present invention when taken in conjunction with the accompanying drawings.